Fatty acyl isethionates (e.g., cocoyl isethionates) are anionic surfactants highly desirable in personal care skin or hair cleansing products, particularly in personal care products, because they lather well, are generally mild to the skin and have good emollient properties. Typically, fatty acid isethionates are produced by esterification of fatty acids or by reaction of fatty acid chloride having carbon chain length of C8 to C20 with isethionate. A typical fatty acyl isethionate surfactant product (e.g., commercially sold or made surfactant product) contains about 40 to 95 wt. % fatty acyl isethionate, and 0 to 50 wt. %, typically 5 to 40 wt. % free fatty acid, in addition to isethionate salts, typically at less than 5%, and trace amounts (less than 2 wt. %) of other impurities. In the present invention, since low total amounts of isethionate product are used, it has been found critical that there be present minimum levels (greater than 15%, preferably greater than 20%) of fatty acid/fatty soap, as percent of the product, and in addition, that greater than 50% preferably greater than 60% of these fatty acid/soaps in the product be of chain length C16-C20 (e.g., to preserve mildness). Specifically levels of long chain in the product (calculated by multiplying total fatty acid/soap in the product by the % of long chain) should be greater than 7.5%, preferably greater than 10%.
In a previous application, U.S. Ser. No. 11/958,471, applicants claimed the use of compositions comprising 3 to 45% by wt. fatty acyl isethionate product and 4 to 20% by wt. C8 to C20 total linear fatty acids and/or fatty soaps in the total composition. By ensuring that fatty acids/fatty acid soaps of a length of greater than C14 comprise 20 to 70% of total linear fatty acid/fatty acid soap and that ratio of total linear fatty acid/fatty soap to total synthetic surfactant was within defined ranges, applicants in that application were able to ensure consistent viscosity at both high and low temperatures.
That application was particularly concerned with utilizing fatty acyl isethionate products which might contain relatively large levels (e.g., at least 10% of product) of free fatty acid.
In that reference, never was there used less than 4% by wt. of a fatty acid isethionate product (4% used in Example 13) and in that example, there was also used at least 4% free fatty acid (e.g., 4% lauric acid) and certainly more since there is also some fatty acid present in the fatty acyl isethionate product itself.
It was never contemplated to use low levels of acyl isethionate product and low levels of total fatty acid because the expectation of one skilled in the art would be that use of less fatty acyl isethionate product would lead to lower foam values. Quite unpredictably, however, applicants have found that it is possible to use lower levels of fatty acyl isethionate product (maintaining benefits of such products at lower cost) while retaining good foam, but only if the level of total free fatty acid/fatty soap is maintained below 4% and the total level of C16 to C20 fatty acid/fatty soaps is in the range of 0.1 to 2%, preferably 0.3 to 1.5% in order to provide both mildness and good lather. Thus, counterintuitively, applicants are able to use both less acyl isethionate product and less free fatty acid (indeed unpredictably applicants have found they must use less fatty acid) in order to ensure good foaming.
Applicants are aware of no reference in the art which teach or suggest low levels of acyl isethionate product in combination with ceiling levels of free fatty acid/soap (from combined acyl isethionate product and free fatty acid/soap in total composition) in order to ensure superior foaming relative to otherwise identical compositions having higher total free fatty acid/soap.
Other references which may be broadly related include:
U.S. Pat. No. 5,415,810 to Lee; U.S. Pat. No. 5,739,365 to Brody; U.S. Publication No. 2004/0274863; U.S. Pat. Nos. 5,952,286 and 6,077,816 to Puwada; U.S. Pat. Nos. 5,132,037, 5,234,619 and 5,290,471 to Greene et al.
Applicants have also filed, in addition to U.S. Ser. No. 11/958,471 noted above, additional applications in this general area as noted:
Ser. No. 11/613,617
Ser. No. 11/613,696
Ser. No. 11/613,666
Ser. No. 11/850,159
Ser. No. 12/235,955.
As indicated, none of the references discloses 0.1 to less than 4%, preferably 0.5 to less than 4%, preferably 0.5 to 3.8% by wt. fatty acid isethionate product which must be used in combination with 0.1 to less than 4%, preferably 0.3 to 3.8% total free fatty acid/soap (from combined product and free fatty acid/soap); and where the total amount of long chain C16 to C20 fatty acid/soap is in the range of 0.1 to 2%, preferably, 0.3 to 1.5% in the liquid composition of the invention. Moreover, none of the references recognizes that, only when total free fatty acid/soap is maintained at these levels will foam be unexpectedly enhanced in otherwise identical (e.g., in terms of co-surfactant, emollient, cationic polymer, etc.) compositions. This is counterintuitive because one would want to use more of fatty acid isethionate product to enhance foam.
As indicated, applicants have been able to achieve this goal at least in part (while retaining good mildness) by utilizing isethionate products which have relatively large amounts of free fatty acid/soap (greater than 15%) of which C16 to C20 comprise >50% such that total levels of long chain length is greater than 7.5% preferably greater than 10% of the product.